A boot made of rubber or resin is used as a part in automobiles. In this specification, a boot includes a cylindrical member such as a hose and tube. A boot band made of a metal belt is used to fasten a boot to another member, by clamping the ear part of the boot band so as to achieve the fastening (see Patent Documents 1 and 2). The boot band has a structure such that the band member (a pressed strip) is wound in its longitudinal direction so that one end of the band overlaps its other end.
Specifically, as shown in FIG. 1, a band 1 is provided with engagement holes 5a, 5b, 5c between the band's ear part 4 (bent into the shape of a box) and the band's edge 3 in the longitudinal direction of the band's overlapping part 2. The ear part 4 consists of legs 41a, 41b and a bridge 42, and is formed so as to protrude outward in the radial direction of the band 1 on the overlapping part 2 The overlapped part 6 is provided with a flattened part 8, whose thickness decreases towards the edge 7 of the overlapped part 6, and engagement claws 9a, 9b, 9c, which engage with said engagement holes 5a, 5b, 5c, protruding outwards in the radial direction of the band 1 after being inserted into said engagement holes 5a, 5b, 5c. 
One procedure for fastening the boot band of this type, as shown in FIGS. 2 and 3, is to use a clamping tool 10 to clamp the ear part 4 so as to plastically deform said ear part 4 by forcing the legs 41a and 41b of the band 1 to become shorter, by applying load from the outside (in terms of the band's longitudinal direction) of the legs 41a and 41b. The deformation of the ear part 4 shortens the length of the band 1 and enables the boot to be fastened to the member to which it is to be fastened. Control of such clamping is carried out as described below:
When the clamping load to be applied to the ear part 4 is constant, a band whose diameter is large (i.e., whose length is long), the difference between the band's diameter and the boot's diameter is large. However, because the extent to which the ear part 4 can be deformed is constant, the extent to which the diameter of the band can be reduced is constant regardless of size of the diameter of the band; that is to say, the extent to which the diameter of the band can be reduced=[initial distance between the legs of the ear part, 10 mm−the distance between the legs when the legs are in close contact with each other, 0 mm]/p=less than Φ3 mm. Therefore, the extent to which a large diameter band fastens a boot is smaller than that of a small-diameter (short length) band, and therefore the reaction force from the boot is smaller. FIG. 4 shows the relation between the clamping load and the distance between legs in cases of a very-large-diameter band, a large-diameter band, and a small-diameter band, assuming that the distance between the legs 41a and 41b before clamping (initial distance between the legs) is 10 mm. As shown in FIG. 4, in the case of a large-diameter band, the distance of the legs of the ear part after clamping (here, this distance is called the M value) tends to be less because the boot's contraction (the boot's reaction force)—which prevents deformation of the ear part—is small. In contrast, in the case of a small-diameter band, the M value tends to be larger because the clearance between the band and the boot is so small that the contraction of the boot (reaction of the boot) is large. In this connection, by controlling the M value, it is possible to determine how large or small the diameters—in other words, the approximate diameters—of the components (such as band and joint) should be. In the process of fastening bands in a mass-production line, the M value is used—as an alternative for a value that represents a change in the diameter of a fastened band—to control the range of diameters of the components.
Patent Document 1: International Publication WO 00-70260 (FIG. 1). Patent Document 2: U.S. Pat. No. 4,299,012 (Specification).
In the step of confirming the M value in the process of fastening the band by clamping the ear part as shown in Patent Documents 1 and 2, the decision as to whether the fastening is good or not is made using an inspection tool such as a gap gauge or a slide gauge. However, confirmation of the M value is very difficult, because the distance (gap) between the legs of the ear part—which must be measured in order to obtain the M value—is about 2 mm after clamping, and there is much structural hindrance due to the members to be connected, such as the lips of both an outer race 12 and a boot 11, as shown in FIG. 5. Therefore, the process—getting the inspection tool, measuring the gap, and putting away the tool—takes a very long time, resulting in very poor productivity. Further, to determine whether the fastening state is good or bad only by referring to the M value has limitations, because the rising parts of the legs 41a and 41b of the ear part 4 elongate due to plastic deformation caused by the clamping. However, to accurately measure the diameter of the band 1—as an alternative to confirmation of the M value—is even more difficult than measuring the M value.
One of the features of the boot band in Patent Document 1 is that—in order to prevent over-fastening that can cause breakage of a boot—engagement holes are provided so that the band has portions that have the smallest cross-sections (i.e., weakest portions) and that stretch when the band is being fastened, and because of which the amount of fastening on the boot can be suitably adjusted.
However, in the case of the band disclosed in Patent Document 1, either (1) a band that has a diameter smaller than the lower limit of the standard diameter, or (2) a joint that has a diameter larger than the upper limit of the standard diameter causes a large amount of fastening on the boot, so that the reaction force of the boot increases. The weakest portion stretches greatly due to plastic deformation, and the M value becomes small although the apparent diameter does not change. Accordingly, the M value becomes similar to that in a case in which there is no stretching caused by plastic deformation, and therefore it is not possible to detect if the diameter of either the boot or the joint is not standard. In this case, the band experiences stronger-than-normal tension, and therefore the band's weakest part can break. In order to assess the band's condition when the band's weakest part has elongated due to plastic deformation, it is necessary to determine both the M value and the extent to which the engagement hole 5a (weakest part) has elongated by visually inspecting the appearance of the band after fastening. Although the M value is used as an alternative characteristic instead of the change in the diameter of the band after it has been fastened, the elongation of the band due to plastic deformation affects the actual size, so that any abnormality of the size of the components cannot be detected, resulting in uncertainty and unreliability of the M value used as a measuring means of the components. It is desirable that the characteristic value for controlling the fastening of a clamping-type boot band be a value that directly reflects changes in the diameter of the band.
The present invention has been made to solve the problems described above, and the objective of the present invention is to provide a clamping-type boot band that enables (1) direct measurement of changes in the diameter of the band during the process of fastening the band, and (2) easy and accurate judgment as to whether a fastening state is good or bad without needing to use a measuring tool.